Make sure that when a SupportsUserData is destroyed, objects destroyed transitively see it as empty.

base/base.gyp

 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
   'variables': {
     'chromium_code': 1,
   },
   'includes': [
     '../build/win_precompile.gypi',
@@ skipping 560 matching lines @@
         'strings/string_number_conversions_unittest.cc',
         'strings/string_piece_unittest.cc',
         'strings/string_split_unittest.cc',
         'strings/string_tokenizer_unittest.cc',
         'strings/string_util_unittest.cc',
         'strings/stringize_macros_unittest.cc',
         'strings/sys_string_conversions_mac_unittest.mm',
         'strings/sys_string_conversions_unittest.cc',
         'strings/utf_offset_string_conversions_unittest.cc',
         'strings/utf_string_conversions_unittest.cc',
+        'supports_user_data_unittest.cc',
         'sync_socket_unittest.cc',
         'synchronization/cancellation_flag_unittest.cc',
         'synchronization/condition_variable_unittest.cc',
         'synchronization/lock_unittest.cc',
         'synchronization/waitable_event_unittest.cc',
         'synchronization/waitable_event_watcher_unittest.cc',
         'sys_info_unittest.cc',
         'system_monitor/system_monitor_unittest.cc',
         'task/cancelable_task_tracker_unittest.cc',
         'task_runner_util_unittest.cc',
@@ skipping 897 matching lines @@
             'base_unittests.isolate',
           ],
           'sources': [
             'base_unittests.isolate',
           ],
         },
       ],
     }],
   ],
 }